Electromagnetic switch



March 18, 1958 A. J. GIRDWOOD ETAL ELECTROMAGNETIC swI'rcH Filed April28, 1955 FIG. 3

INVENTORS ARTHUR J. GIRDWOOD ROBERT G. KOCH BY A TORN Y United StatesPatent ELECTROMAGNETIC SWITCH Arthur J. Girdwood and Robert G. Koch,Guelph, Ontario, Canada, assignors to Leland Electric Canada Limited, acorporation of Canada Application April 28, 1955, Serial No. 504,523

7 Claims. (Cl. 20087) This invention relates to improvements in circuitcontrol mechanisms, and more particularly relates to a starting switchfor a dynamo electric machine.

It is desirable when starting many types of dynamo edectric machines toemploy a starting winding in addition to the main operating winding inorder to increase starting torque. Such an auxiliary winding furtherserves to reduce excessive flow of current through the main winding witha consequent reduction in the danger of winding burn out. In the past,centrifugally operated switches have been used to connect and disconnectthe starting winding at the proper time, but such switches areunreliable, require an undue amount of mechanical maintenance, and areparticularly subject to arcing and pitting of electrical contacts.Relays, actuated by portions of the magnetic circuit of the dynamoelectric machine for which they are adapted to control, have been usedfor this purpose. These relays are generally complicated in structure inorder to insure fast pull out at the proper point on the dynamo electricmachines starting curve, and are not easily adaptable for use with anyelectrical machine. Also, such relays have a tendency to vibrate andcreate excessive buzzing when employed with alternating currentmachines, and require complex structures to reduce unwanted vibration.

It is, therefore, an object of the present invention to provide anelectromagnetic mechanism for switching selected winding portions ofdynamo electric machines having a magnetic circuit mechanicallyenergized by a portion of the windings of the machine.

It is another object of the invention to provide an electromagneticswitch free from magnetically induced vibration for operating on eitheran A. C. or D. C. type of dynamo electric machine.

It is a further object of the invention to provide an electromagneticswitch having a small differential between the amount of magnetic fieldcurrent required for opening and closing of the switch contacts.

It is yet another object of the invention to provide an electromagneticswitch for dynamo electric machines which is easy to manufacture and lowin cost.

For a better understanding of the invention, together with other andfurther objects thereof, reference is made to the following detaileddescription taken in connection with the accompanying drawings, inwhich:

Fig. 1 is an isometric view of the invention.

Fig. 2 is a plan view of a switch embodying the principles of theinvention.

Fig. 3 is a side elevation of the switch as seen from line 3--3 of Fig.2.

In the drawings, in Fig. 1 is shown a portion of an end of a stator fora dynamo electric machin to which the switch may be adapted. The machine10 has conventional stator slots 12 with the usual coils 14 embeddedtherein for producing magnetic flux.

Larger types of machines to which the invention is particularlyadaptable, generally have end portions of the main winding coilsextending slightly beyond the surface of the end laminations of thestator. Thus, as shown in Fig. 1, winding 14 of motor 10 extendssufiiciently beyond the end lamination 16 of the stator to allow aU-shaped strap or bar 18 to partially encircle it. The open ends ofstrap 18 are held in position by a mounting member or bracket 20 whichmay be suitably fastened to the stator 12 or to some portion of theframe of motor 10 by means of suitable screws or fasteners 13. As heavystarting current passing through winding 14 induces a large magneticflux in strap 18, no separate windings are needed for creating therequired magnetic field.

An armature 22 is provided which is pivotally mounted to bracket 20 by asuitable pin 24 intermediate the ends of the armature and spacedtherefrom by spacer 25 (Fig. 3). Armature 22 is adapted to rotate aboutpin 24 when a current passes through winding 14. Armature 22 has aprojection or notched portion 26 along one longitudinal edge which formsa stop for receiving and securing the shorter end 27 of bent leaf spring28. Spring 28 may be formed from any resilient strip material which iscapable of having a portion thereof bent back upon itself so as to liealong the edge 30 of armature 22 and be held securely in position byprojection 26. Armature 22 has slots 34 near each end thereof which arespaced so as to receive the end portions 32 of strap 18 when thearmature is rotated about pivot pin 24.

It is desirable in motor starting switches that the contacts breakimmediately when the motor has reached that point on its starting curvewhere the starting windings should be disconnected. In the presentinvention fast action between the making and breaking of the relaycontacts is assured by correlating the torque curve of the armature 22with that of the spring 28 so that there is only a small diiferentialexisting between them. A correspondingly small differential then existsin the amount of current supplied by winding 14 for setting up amagnetic field in strap 18 which actuates armature 22.

To provide this torque, slots 34 are shaped and contoured so that thegap in the magnetic path between end portions 32 and armature 22 isvariable and decreases as armature 22 rotatably progresses towardsengagement of the slots 34 with the end portions. Any desiredconfigurations of the slots may be used which will insure a smalldifferential between making and breaking of the switch contacts. Forexample, the armature slots 34 shown in the drawings have their lengthdivided into a square portion and a somewhat curved portion whereby themagnetic reluctance is decreased and armature torque increased tocounter the increased spring force, as armature 22 progresses towardsits closed position. The end portions 32 of magnetic strap 18 are curvedin a concave fashion to properly cooperate with the shaped slots.

34. Strap 18 may be channeled near the end portions 32 so that it may besprung or snapped into a firmly held position in engagement with thewalls of slots 36 in member 20, when the end portions 32 are passedtherethrough; It is understood that the armature may be made to actuateany of a number of conventional contact arrangements. For purposes ofillustration, a single pair of normally open contacts are shown. Thesecontacts may be connected in series with a conventional auxiliarystarting winding and associated circuit on the dynamo electric machineso that the starting winding is energized when the contacts are closedduring periods of high starting current. Of course, for some startingcircuit applications, the contacts may be a conventional, normallyclosed type which are adapted to open during periods of heavy armaturecurrent. i

Contacts 38 are fastened near the ends of a pair of.

40. A spring stop or backing member 42 is mounted adjacent to the outerstrip 41 so as to provide positive closing and a wiping action betweenthe contacts, since strip 41 tends ot bend around the end of backingmem- -ber42 as pressure from armature 22lincrea-ses. :A suitableinsulating spacer 4 is secured near the bent endof spring 28 to urgecontacts 38 into-engagement with each other, therebyconnecting'the-st-arting windingtoa source of power when armature 22 isrotated towards the ends 32'of bar '18. The 'leaf contacts 38,insulating spacer 40 and backing member 42 are secured to upright tabportion 48 of insulating strip 20 bymeans of bolts, rivets or othersuitable fastenings 46. -When motor 14) is in a running condition,only-a relatively small current is carried by themain windings '14.Therefore, armature 22 is in an open or passive position, and thestarting windings are de-energized.

During running periods, the relatively low alternating current carriedby windings 14:is sufficient to cause-armature 22 to vibrate slightlyin'accordance with the A. C. voltage cycle so that an annoying buzzingis capable of being generated. However, such noise is eflectivelyeliminatedand vibration reduced to a'negligible amount by the dampingaction provided by the pressure of the bent back portion'of spring 28against edge 30 of armature 22. All tendency .ofarmature22 to vibrate isabsorbed by spring 28. t

In operation, azheavy current passes through windings 14 when power isapp'liedto-themotor for starting purposes. This surge of current inducesa large magnetic flux through Urshaped strap 18 which causes armature 22to rotate. inwardly towards'end portions 32 to close the gaptherebetween. Consequently, spring 28 is urged laterally againstcontacts '38, causing them to close with a positive action. As pressureisapplied to spring .28 by armature 22, the resulting wedging action ofspring 28, as its free end tends to straighten up,..increases thepressure between contacts 38 and desirably reduces the contactresistance.

Since the pull-in torque curve of armatureZZ has been selectivelyshaped, :the differential existing betweenthe amount of currentfiowingin windings. 1.4Land. required to close :and'open-contacts 38. issmall. As soon asithe motor reaches the:.desired:.point;in its operatingcurve where the starting current has decreased appreciably, to whichpoint the torque ..curve of armature.22 may .becorrelated, thecontactstare .opened andthe starting .winding connected thereto isdisconnectedrfromihe .source of. p.ower,.,allowing the;motor'to.reachfinal :operating speedzin normal fashion.

Although ;for; purposes ofillustration: the .invention. hasheen;described;in combination with. an A..C.:machine,tyet therswitch maybeused with any type :of dynamoelectric machine, whether A. C.- or D...C., .as longrassa portion of; a windingcarryingiheavy startingcurrents is available for providingrth'exurrent for creating themagneticoperatingfiuxzofrthesswitch. In.D. C. machinestheswitch would :be;actuated by armature ..current which requires eitherza monntingon'ztherotating portion of, the machine or in some other convenientportion of the armature circuit where itsiheavy starting current may beproperly utilized.

While the present invention has been disclosed .by means of specificillustrative embodiments thereof, it would be obvious to thoseskilled inthe art that various changes and modificationsin the means'of operationdescribed or in the apparatus, may be made withoutdepartingfrom thespiritzof the invention:asidefinedtin the appended claims.

Weclaim:

;1..-A .magnetic control :device for :starting a :dynamo electricmachine having a main operatingzwindingiandza starting winding:comprisingza :.core :of magneticzmaterial partially .isurrounding a:portion :of ;said .main windings andadapted'to set up :ama-gnetic fieldwhen current passes through .said windings, .said ;core having ra pairoft'out- Wardly extending poles, an armature member pivotally mountedintermediate the ends thereof and rotatably operable to vary themagnetic field set up between said poles, a leaf spring for biasing saidarmature away from said poles, said leaf spring having a portion bentback upon itself, the smaller end of said bent portion of said springbeing pivotally connected to an edge of said armature whereby saidspring urges said armature away from said poles, said armature ends..having slots therein adapted to rotatably .receive .said outwardlyextending poles, said slots having selectively shaped contours toprovide a variable magnetic force between said poles and said armatureduring rotation of said armature ends towards said polesso that thedifferential between the armature pulling torque of said field andopposing torque of said spring is substantially constant throughout thepath of travel of said armature, and contacts for operatively connectingsaid starting Winding resiliently mounted adjacent. saidspring,and;adapted to beurgediinto .an operative position by movement ofsaid spring away 'from said poles.

2. Amagnetic'control device forstarting a dynamo electricmachineshaving. a main operating winding-and a starting windingcomprisingia U'-'shaped core of magnetic materialshaving azportion ofsaid magnetic windings passing:between the'arms:.of said .U andadapted'toset-up a magnetic. field whenzcurrent passes throughsaidtwindings, the upper portions. of the arms. of. said U beingslightly curved .to -forma .pair of :mag netic poles, a mounting strapfor saidzcore having'apair ofwslots'nearthe outer end ofisaidstrapandi-adapted to secure said upper portions .of .said arms .in anupright position when saidportions are wedged in said slots, an armaturemember pivotally attached to :said mounting strap intermediatethe:ends'of said armature and'rotatablyoperable to vary the magneticfield set up between said poles, spring means for'biasing said armatureaway fromsaid-poles, saidarmaturehaving slots adapted to receivesaidpoles, said armature slots'having selectively shaped contours to providea variable magnetic force between said poles and said armature duringrotation of said armature ends towards said polesso that thedifferential between the armature pulling torque of said field andopposing torque of said springis substantially constant throughout thepath of travel of said armature, and contacts for operatively connectingsaid starting winding resiliently mounted adjacent said springfmeans andadapted to be urged into an operative position by movement of -saidspring means away from said poles.

.3..A :rnag-netic control device for starting a dynamo electricmachine-having a main operating winding and a starting windingcomprising-a 'core of magnetic maten'al partially surrounding a portionof saidmain windings and adapted to setup =-a magnetic field whencurrent passes throughsaid windings,- saidcore having a pair ofoutwardly extending poles, anarmature member pivotally mountedintermediate the ends thereof and rotatably operable-to-varythemagneticfield set up between said poles, spring means "for biasingvsaid'armatureaway from saidpoles, said armature having. slots adaptedtorotatablyreceive said outwardly xextendingpoles, atxleast one of said"slots"haVingJa configuration comprising a square portion and a curved,portion constructed and arranged to provide a selectivelyvariablemagnetic-force between said poles'an'd said armatureduringrotation of said armature ends toward saidtpoleswherebyzthedifferential between the armature pulling torque of saidv-field and.

opposing ..torqueof, saidspring is substantially constant throughout..the ,path ,of vtravel not .said armature, and contacts. fortopenativelyconnecting?- said starting winding resiliently rmounted adjacent gsaid:spring :means and adapted to be urged intozan;operativetposition:by'movement: ofzsaid springgmeans' away fromzsaid poies.

.4. A :magnetic zcontrol fld eviceioristarting' a vdynamo electricmachine having:a: maimoperatingi winding and a starting Windingcomprising a 'U-shaped core of magnetic material having a portion ofsaid magnetic windings passing between the arms of said U and adapted toset up a magnetic field when current passes through said windings, theupper portions of the arms of said U bcing slightly curved to form apair of magnetic poles, a mounting strap for said core having a pair ofslots near the outer end of said strap and adapted to secure said upperportions of said arms in an upright position when said portions arewedged in said slots, said strap having an upwardly extending tabportion along one edge of said strap and attached near the inner endthereof, an armature member pivotally attached to said mounting strap ata point intermediate the ends of said armature and rotatably operable tovary the magnetic field set up between said poles, spring means forbiasing said armature away from said poles, said armature having slotsadapted to rotatably receive said poles, said armature slots havingselectively shaped contours to provide a variable magnetic force betweensaid poles and said armature during rotation of said armature endstowards said poles so that the differentil between the armature pullingtorque of said field and opposing torque of said spring is substantiallyconstant throughout the path of travel of said armature, and contactsfor operatively connecting said starting winding resiliently mounted tosaid upwardly extending tab portion of said strap adjacent said springmeans and adapted to be urged into an operative position by movement ofsaid spring means away from said poles.

5. A magnetic control device for starting a dynamo electric machinehaving a main operating winding and a starting winding comprising aU-shaped core of magnetic material having a portion of said magneticwindings passing between the arms of said U and adapted to set up amagnetic field when current passes through said windings, the upperportions of the arms of said U being slightly curved about theirlongitudinal axes to form a pair of magnetic poles, a mounting strap forsaid core having a pair of slots near the outer end of said strap andadapted to secure said upper portions of said arms in an uprightposition when said portions are wedged in said slots, said strap havingan upwardly extending tab portion along one edge of said strap andattached along the inner end thereof, an armature member pivotallyattached to said mounting strap at a point intermediate the ends of saidarmature and rotatably operable to vary the magnetic field set upbetween said poles, said armature having an outwardly extendingprojection along one edge, a leaf spring for biasing said armature awayfrom said poles, said leaf spring having a portion bent back uponitself, the smaller end of said bent portion of said spring beingadapted to cooperatively engage said projection whereby said springurges said armature away from said poles, said armature ends havingslots therein adapted to rotatably receive said poles, at least one ofsaid slots having a configuration comprising a square portion and acurved portion constructed and arranged to provide a selectivelyvariable magnetic force between Said poles and said armature duringrotation of said armature ends toward said poles thereby thedifferential between the armature pulling torque of said field andopposing torque of said spring is substantially con stant throughout thepath of travel of said armature, and normally open contacts foroperatively connecting said starting winding when the current throughsaid main winding increases to a predetermined value, said contactsbeing resiliently mounted adjacent said spring and adapted to be urgedinto an operative position by movement of said spring away from saidpoles, said armature and said contacts being adjusted to disconnect saidstarting winding when the current through said main winding decreases toa preselected value.

6. A magnetic switch comprising a magnetic core having means for settingup a magnetic field therein, said core having a pair of outwardlyextending poles, an armature member pivotally mounted intermediate theends thereof and rotatably operable to vary the magnetic field set upbetween said poles, a resilient spring member for biasing said armatureaway from said poles, said spring member having a portion bent back uponitself, said bent back portion having a free end pivotally connected toan edge of said armature whereby said spring member urges said armatureaway from said poles, and contacts resiliently mounted adjacent saidspring member and adapted to be urged into an operative position bymovement of said spring member away from said poles.

7. A magnetic switch comprising a magnetic core having means for settingup a magnetic field therein, said :eore having a pair of outwardlyextending poles, an armature member pivotally mounted intermediate theends thereof and rotatably operable to vary the magnetic field set upbetween said poles, a resilient spring for biasing said armature awayfrom said poles, said spring having a bent portion defining first andsecond spring members, said first spring member having an end pivotallyconnected to an edge of said armature and disposed lengthwise inabutting relationship with said edge of said armature, and contactsresiliently mounted adjacent said second spring member and adapted to beurged into an operative position by movement of said spring away fromsaid poles.

References Cited in the file of this patent UNITED STATES PATENTS649,031 Young May 8, 1900 1,053,340 Ziegler Feb. 18, 1913 1,220,813Barrow Mar. 27, 1917 2,428,784 Cole Oct. 14, 1947 2,503,493 Juhasz Apr.11, 1950 2,629,031 Ballman Feb. 17, 1953 2,629,792 Fitch Feb. 24, 1953FOREIGN PATENTS 470,649 Germany Ian. 26, 1929

